Prior art FIG. 1 is a top perspective view an LED package 10 copied from the present assignee's U.S. Pat. No. D598,871, incorporated herein by reference. The commercial name for the package is the Rebel™. The package 10 is about 3 mm per side. The package 10 contains a square LED die whose sides are aligned with the sides of the package 10. The center axis of the LED die is along the center axis of the hemispherical lens 12. Anode and cathode electrodes are on the bottom surface of the package 10 for soldering to metal pads on a printed circuit board. Anode and cathode electrodes formed on the LED semiconductor layers are electrically connected to the anode and cathode electrodes on the bottom of the package. Typically, the LED layers are mounted on a submount, and the submount electrodes are, in turn, connected to the package electrodes. LEDs and submounts are described in detail in U.S. Pat. No. 7,452,737, assigned to the present assignee and incorporated herein by reference. The emitted light pattern is substantially Lambertian, which forms a circle on a flat surface directly above the package 10.
FIG. 2 is a top down view of the package 10 showing the alignment of the LED die 14 with the lens 12 and package 10.
FIG. 3 is a side view of the package 10 along the diagonal line 3-3 in FIG. 2. In the example of the assignee's actual package 10, the hemispherical lens 12 has a diameter about 2.55 mm, and the LED die 14 is about 1 mm per side. The diagonal length of the LED die is about 1.4 mm. In FIG. 3, the edges of the actual LED die 14 are shown by solid lines. Since the lens 12 is a hemisphere referenced to the top surface of the LED die 14, light rays 15 emitted from the center point 16 of the LED die 14 at all angles impinge on the surface of the lens 12 at substantially right angles, so the light rays 15 are emitted from the package 10 with virtually no internal reflection and no refraction. As the source of light along the LED die surface moves away from the center point 16, the maximum refraction increases since all the light rays do not impinge on the lens 12 surface at right angles. The size of the package 10 and lens 12 are designed for an LED die 14 having maximum sides of about 1 mm to substantially prevent any light rays from being internally reflected by the lens 12.
For example, FIG. 3 illustrates an extension of the LED die 14 in dashed outline and a light ray 18 emitted near the corner of the enlarged LED die. The angle of the light ray 18 is less than the critical angle, resulting in total internal reflection (TIR) of the light ray 18. Such light is thus wasted. Accordingly, the width of a square LED die for use with the package 10 is limited to about 1 mm (the solid outline of the die 14) in order to minimize TIR.
FIG. 4 is a top perspective view of another prior art package 20 by the assignee having the same width and lens 12 as the package 10 of FIG. 1 but a longer length. The diameter of the lens 12 is limited by the width of the package 20.
In some applications, there is a need for greater light output using the same package 10, where the electrode footprint and outer dimensions of the “higher output” package need to be the same as those for the existing package 10. The substantially Lambertian emission pattern also needs to be substantially the same. Although a larger width LED die may be used to emit more light, there will be TIR within the hemispherical lens 12 if a larger LED die is used, greatly reducing the efficiency of the package. The diameter of the hemispherical lens 12 cannot be increased without increasing the width of the package 10.